Current alpha-olefin production processes yield large molar quantities of 1-butene, which has limited value. Thus, ways to avoid making 1-butene or to convert 1-butene into higher value products are desired. Catalysts have been used to dimerize 1-butene to octenes, but the selectivity of the catalysts for the more desired linear internal octene isomers is low, and the activity and conversion of the catalysts are low as well. A catalyst that is active and selective for dimerization is desired. The products may be used as precursors for production of plasticizers. Since 1-pentene, 1-hexene and 1-octene are also low molecular weight alpha olefins; they can also be dimerized for making linear internal olefin dimers.
Currently, vinylidenes can be produced using triisobutylaluminum to catalyze alpha olefin dimerization. In one embodiment, the reaction can use 0.5 weight percent triisobutylaluminum, take 4 to 6 hours, and be conducted at 170 to 220.degree. C. Under these conditions, the reaction gives approximately 70 percent alpha olefin conversion. The converted product includes 80 to 90 weight percent vinylidene and 10 to 20 weight percent internal dimer olefins. Such a process is severely limited by high vinylidene olefin selectivity. Additional process disadvantages include a long reaction time and a high thermal requirement.
Alpha olefin dimerization technology to produce vinylidenes is known. In a preferred embodiment, the catalyst used in the technology is composed of bis(cyclopentadienyl)zirconium dichloride and an alumoxane in a molar ratio of 1:4 at a 1000:1 olefin:aluminum molar ratio at 40.degree. C. Under these conditions, the reaction gives 93 percent alpha-olefin conversion in two hours. The converted product includes 95 weight percent dimer olefin and only 2 weight percent internal olefins. A disadvantage of this catalyst system is that it produces very little internal olefins. With proper catalyst selection, even under the most reasonable conditions, the internal olefin selectivity would still not make it economically feasible as a means of producing internal olefins.
The use of an alkylaluminum catalyst, 1 to 4 mole percent, at 100 to 140.degree. C. has been disclosed. Specifically, the use of trioctylaluminum as the catalyst is disclosed. In a preferred embodiment of the patent, the catalyst concentration is 1.7 mole percent at 120.degree. C. Under these conditions, the reaction gives a 90 percent alpha olefin conversion in 192 hours. The converted product includes 99 weight percent alpha olefin dimers, 95 weight percent vinylidene, and only 4 percent internal dimer olefins. Though the patent technology offers good dimer olefin selectivity, this patent does not represent an efficient manufacturing process due to the long reaction times and production of vinylidene olefins. Reaction times could be reduced by increasing the alkylaluminum catalyst concentration, increasing the reaction temperature, or reducing the conversion goal to less than 90 percent conversion. However, the reaction times would still be too long to provide a reasonable manufacturing process.
A catalyst system composed of bis(cyclopentadienyl)-zirconium dichloride, an aluminoxane other than methylaluminoxane (all examples use isobutylaluminoxane), and trimethylaluminum has also been disclosed. In a typical example, the catalyst system is approximately 7.5 mmoles aluminum (3.9 mmoles aluminoxane and 3.7 mmoles trimethylaluminum) and 0.11 mmoles of bis(cyclopentadienyl)zirconium dichloride and reacts with 128 mmoles of olefin at 50.degree. C. Under these conditions, the catalyst gives a 92.7 percent alpha olefin conversion in six hours. The converted product includes 90 weight percent dimer vinylidene olefin and only 7 weight percent internal olefin. This system also has the disadvantage of producing vinylidene olefins and not enough internal olefins.
A method of manufacturing alpha-olefins by contacting ethylene with an iron complex of a selected 2,6-pyridinedicarboxaldehyde bisimine or a selected 2,6-diacylpyridine bisimine is also known. Although the catalysts used in this method are closely related to the catalysts used in the present invention, this method has not been connected with the dimerization of olefins. Rather, this method deals with the manufacture of alpha-olefins from ethylene.
In contrast, Applicants have achieved a process of dimerizing .alpha.-olefins using, as a pre-catalyst, a tridentate bisimine ligand coordinated to an iron center. This pre-catalyst is activated by the addition of a co-catalyst, which may be an alumoxane or a combination of a Lewis acid and an alkylating agent. Once activated, the catalyst dimerizes .alpha.-olefins rapidly to form a mixture of linear, internal olefin dimers and methyl-branched internal olefin dimers.